Method for heating asphalt concrete roadways and the like

ABSTRACT

Disclosed herein is a method for heating asphalt concrete roadways during paving and/or repaving thereof. The road surface is heated by directing a flame across a radiant heating element which is to be heated. Heating of the road surface is accomplished by radiant heat of red and infra-red heat energy, and such radiant heat will penetrate the road surface to a depth of one inch or more whereupon the heated and softened asphalt together with portions thereof beneath the heated portion are excavated to be reworked and again deposited as a new road surface. The addition of extra new quantities of asphalt material can be introduced if desired.

Elnite States Patent Cutler Apr. 30, 1974 [54] METHOD FOR HEATINGASPHALT 1,952,452 3/ 1934 Monroe 404/95 CONCRETE ROADWAYS AND THE LIKE2,705,906 4/1955 Fiuell 404/95 3,132,642 5/1964 Fingland.... 126/2712 AInventor: Earl R Cutler, Lawrence. Kans- 3,311,104 3/1967 w611ner.....126/2712 AX Assigneez Cutler p g Associates, 3,096,696 7/1963 Reisser126/2712 A X Incorporated, Lawrence, Kans. Primary ExaminerNile C.Byers, Jr. [22] plied: 1972 Attorney, Agent, or Firm-Olson, Trexler,Wolters, [21] APPL 2 04 Bushnell & Fosse, Ltd.

Related US. Application Data [63] Continuation-impart of Ser. No.129,404, March 30, [57] ABSTRACT 19711 3,724,445- Disclosed herein is amethod for heating asphalt concrete roadways during paving and/0rrepaving thereof. U-S. Cl. 'I'he road urface is heated directing a flameacross Int. Cl. a di t h atin element is to be heated Heat. Field ofSearch 404/771 79, 95; 126/271' 1, ing of the road surface isaccomplished by radiant heat 126/271 271-3 of red and infra-red heatenergy, and such radiant heat will penetrate the road surface to a depthof one inch References Cited or more whereupon the heated and softenedasphalt UNITED STATES PATENTS together with portions thereof beneath theheated por- 1,9s4,s49 12/1934 Van Allen 404/95 x tion are excavated bereworked and again deposited 3,055,280 9/1962 Neville 126 2712 A as a wroad Surface. The addition of extra new 1,733,841 10/1929 Vincent 404/95quantities of asphalt material can be introduced if de- 2,274,517 2/1942Ashmore... 404/95 X sired 2,273,254 2/1942 Davis 404/95 X 2,048,8137/1936 Porterfield 404/95 6 Claims, 7 Drawing Figures 1| 1 1 lllllili 1Ill 1 PATENTEDAPRBO m4 3,87,888

' SHEET 2 0F 3 METHOD FOR HEATING ASPHALT CONCRETE ROADWAYS AND THE LIKEREFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of myearlier filed copending application Ser. No. 129,404, filed Mar. 30,1971, now U.S. Pat. No. 3,724,445.

BACKGROUND OF THE INVENTION This invention relates generally toresurfacing of roadways, and more particularly to a method of heatingthe roadway at several work stations in a resurfacing machine.

This invention deals with substantial improvements in my earlier filedcopending application Ser. No. 129,404 filed Mar. 30, 1971, and theentire subject matter of this earlier application is included herein byreference. Road surfacing apparatus as set forth in my U.S. Pat. No.3,361,042 provides means for quickly and inexpensively resurfacingroadways made of asphalt concrete materials or the like. The apparatusmay be 8 to 12 feet wide and 40 to 50 feet long and move along theroadway at a relatively slow speed so that during the single continuouspass over the pavement the old road surface in front of the machine isexcavated and converted to a refinished road surface at the rear of themachine. A distinct advantage of repaving roadways with this type ofmachinery is that the finished repaved strip of roadway is immediatelyavailable for vehicular traffic within a matter of minutes aftercompletion.

The road repaving machinery, in which the method of this invention isutilized, performs the following functions during the repaving process.First, the road surface is heated so that heat penetration is obtainedto a depth of one inch or more below the surface of the roadway. This isfollowed by scarifying deeply to excavate and disarrange the materialheated by the first step. Then piling the disarranged material formaximum surface exposure so it can be further heated, this secondheating step being substantially the same as in the first instance.Minor amounts of conventional tack coat to help weld the total hot topmixture to the substraight from which the heated material was removedcan be added. This is followed by tamping and screening which, in turn,is followed by compacting as by conventional rolling means.

Heretofore, heating of the roadway surface was accomplished by a flameand partial radiant heat which produced a nonoxidizing atmosphere sothat the temperature of the road surface could be elevated higher thanthe material could experience in air without being set on fire. Thishigh temperature was needed for maximum heat penetration of the roadsurface. However, to achieve high temperature and penetration of theroad surface, the amount of fuel used for both open flame and radiantheat is substantial.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide a method of heating a road surface wherein the type of heatimpinged upon the road surface is substantially radiant heat so thatmaximum heat penetration is obtained.

Briefly, the method of this invention utilizes a heating apparatus inthe form of two or more work stations carried by a repaving machine. Theheating apparatus is provided with a fuel receiving manifold which ispositioned overa heating chamber and is rectangular in configurationsimilar to that of the heating chamber. A plurality of discrete fuelburning elements have conduit portions extending through the heatingchamber and into the manifold chamber to receive a mixture of hot gasand air which is a combustible mixture that is burned at the heatingnozzle. To achieve the proper pressure and flow of fuel-air mixture, avariable quantity air blower is in fluid communication 'with themanifold chamber sothat delivery of the air-fuel mixture to the nozzleis achieved under controlled velocity conditions. Furthermore, the fuelis preheated to a relatively high temperature before combustion at thenozzle to minimize rapid expansion of the gases during the combustionprocess. Therefore, the pressure within the heating chamber can bemaintained substantially equal to that of the atmospheric pressureoutside the chamber and little or no heat will escape from under theside walls thereof. Also, by maintaining the pressure within the heatingchamber substantially equal to the atmospheric pressure minimum or noair is drawn into the heating chamber from under the side walls andoxidization or actual combustion of the road surface is prevented.

In accordance with the principles of this invention the flame from theheating apparatus is directed downwardly and then deflected laterally orradially outwardly so as to fall across substantially the entire area ofa radiant heating element which converts the heat from the flame toradiant heat. The radiant heating element is positioned adjacent theroad surface and thereby provides red and infra-red heat energy topenetrate the road surface to depths to 1 inch or more, this beingaccomplished in a relatively short period of time andwith minimum use offuel. The radiant heating element is preferably a nickel-base heat andoxidationresistant material such as INCONEL but may be made from anysuitable material.

Many other objects, features and advantages of this invention will bemore fully realized and understood from the following detaileddescription when taken in conjunction with the accompanying drawingswherein like reference numerals throughout the various views of thedrawings are intended to designate similar elements or components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevatio'nal view ofa roadbed resurfacing apparatus utilizing the heater structure whichoperates in accordance with the method of this invention; V

FIG. 2 is a perspective fragmentary view of a heater structure which isused to perform the method of this invention;

FIG. 3 is a side elevational sectional view of the heater structureapparatus of FIG. 2;

FIG. 4 illustrates an air control mechanism for controlling the volumeof air delivered to an air fuel mixing chamber of the heater structure;

FIG. 5 is an enlarged fragmentary view showing a discrete heater unitmounted within the heater structure;

FIG. 6 shows an alternate flame deflector arrangement which can be usedin the heater unit of FIG. 5', and

FIG. 7 is a top view of the heater arrangement of FIG. 3 showing theplacement of the discrete heater units and the associated radiantheating elements together with the'air blower and manifold structurepositioned above the heaterchamber.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT For a betterunderstanding of the method of this invention the apparatus used tocarry it out will be first described in detail. Referring to FIG. 1there is seen a side view of a road resurfacing equipment and isdesignated generally by reference numeral 10. The road recomessubstantially compressible under the weight of roller action. Additionalquantities of asphalt material may be supplied, as desired, tobuild upthe road surface to the previous height or to a height greater than theold road surface. The rate of travel of the machine may be in theorderof 8 to feet per minute thereby providing -a completely reconstructed-raod surface upon which vehicular traffic can commence substantiallyimmediately after the new road surface has been formed. j

A quantity of new material 14 isdelivered via a truck 16 intoa hopper orreceptacle 17' at the front end of the machine. A conveyor 18 along thetop portion of the frame transports the new material from the hopper toone or more various work stations; A control station 19 I is locatedintermediate the machine and an operator is stationed there tocontrolthe direction of travel as well as the rate of travel of themachine. Also, the operator at the controlstation 19 controls variousfunctions such as the'ar'nount of heat supplied to the road surface bythe various burners. One or more diesel'engines 20 are mounted at therear portion of the'machine and include various control panels 20 whichoperate hydraulic pumps or compressors. The wheels 13 are motorized byindependent hydraulic motors operated by a hydraulic hydrostatic supplypump control mechanism which may be-driven from the engines 20. Aplurality of fuel tanks 21 are mounted on top of the support frame 22 ofthe machine and are used to carry fuel supplies for both the dieselengine 20 and for the burners 24 and 26. One or more of the fuel tanks21 may be filled with diesel fuel while one or more of the fuel tanksmay be filledwith pentane fuel for operating the burners. The pair ofroad surface heaters 24 and 26 are spaced sufficiently apart so that theheated road surface can be dug up and rearranged for additional heatingof the dislodged components of the road. The manner in which the roadresurfacing apparatus 10 operates is more fully discussed in my U.S.'Pat. No. 3,36l,042 and no further detailed description of operation isdeemed necessary herein.

The road resurfacing apparatus 10 includes a pair of heaters 24 and 26each constructed substantially in the same manner and therefore only asingle heater will be discussed in detail. The heater 24 includes a heatcham- 4 v g I ber 28 facing downwardly to be positionedimmediately overthe road surface to be repaved so that the road surface can be heatedtoa depth of approximately one inch or more thereby softening the-materialforming the old road surface. After heating of the road surface it isexcavated by scarifyingor the like with a plurality of cutting points orknives and additional heat is supplied by the second burner 26. b

The heating chamber 28 ,is formed by' a' plurality ofchamber-forrning'walls 30 of fabricated construction and a top wall orroof 31. The bottom of the chamber is open and the downwardly extendingperipheral edge portions of the side walls are closely spaced to theroad surface so that minimum air gap is obtained. The pressure withinthe heating chamber 28 is maintained substantially equal to theatmospheric pressure outside of the chamber so thatno heat escapes fromthe space be-.

tween the walls and the road surface, and similarly, no

unwanted oxidizing air -will'be drawn, into the heating chamber from theoutside atmosphere. v

Positioned above the heating chamber 28 is a fuel mixing chamber 32which, in turn, is in fluidcommuni cation with a pressure blower unit33.'Th e-pressure blower unit 33 supplies a quantity 'of air, underslight pressure so that the air fuel'mixture is'direct'ed toward aplurality of burners within the heating chamber 28; While the pressureprovidedby the blower33 is relatively low, the air volume moved by theblower is maintainedvrelatively highfor maximum heating of the burners.The-air fuel mixture supplied from the fuel mixing chamber 32-is thendirected into a distributing manifold 34 mounted on top of "theheating-chamber 28. The air fuel manifold34 preferably takes the form ofa rectangular chamber having acommonwall between the heating chamber andthe manifold-A plurality of upwardly extending large diameter exhauststacks 36 are located at each of the four corners of the burner so thatheat formed within the heating chamber 28 can rise through the exhauststacks and be expelled at a level substantially above'street level sothat'w'orkme'n about the machine arenotsubjected to the extreme heat.

Referring no'w'to'FIG. 2 a detailed fragmentary perspective view, of theheater'24 is illustrated, it being understood that the side ofthe'heater 24 is'typical-with respect to the other side of thehater. Thesidewalls 30 include a pluralityof reinforcing members 37 positionedvertically about theside walls. Atop and bottom edge 38 also formreinforcing members about the side walls. The manifold 34 is in fluidcommunication with an enlarged manifold portion 34a which forms the topwall of the heating chamber. The manifold portion 3411 can be formedeither .as an integral part of the heating chamber as shown, i.e. formedby the top wall thereof, or it can be formed as a separate unit mountedon top of theheating .chambenThe fuel mixing chamber 32 includes a top40 which has a flange 41 fastened thereto for supporting the blower 33The blower 33 has the output portion thereof 33a in direct fluidcommunication with a manually adjustable flow control valve 42. The flowcontrol valve 42 is adjustable to select the proper volume of airdirected to the manifold To insure that the air fuel mixture directed tothe burners within the heat chamber 28 is expanded to the maximumextent, an air heat pipe 43 is in fluid communication between one of theexhaust stacks 36 and the outlet port 33a of the blower 33. In theillustrated embodiment the connection to the outlet 33a is made belowthe flow control valve 42, it being understood that this hot airconnection can be made above the flow control valve, if desired. A fuelline 44 is connected to the fuel mixing chamber 32 and therein the fuel,preferably pentane or the like, is admixed with the air from the blower33 and delivered to the first manifold portion 34 and therefrom to thesecond manifold 34a. The fuel delivered through the line 44 is heated bya preheater unit, to be described hereinbelow, which is mounted withinthe heating chamber 28. Therefore, fuel from the tanks 21 is supplied tothe inlet line 44a and directed through the preheater unit and therefromto the fuel line 44 and into the mixing chamber 32. By so preheating thefuel and heating a portion of the air supplied to .the mixing chamber,maximum expansion of the air fuel mixture is obtained before combustion.This enables the air fuel mixture to ignite with minimum expansion ofgases so that little or no pressure is obtained within the heatingchamber.

Referring now to FIG. 3 there is seen a side elevational sectional viewshowing more clearly the details of construction of the burner of thisinvention. Here it can be seen that the mixing chamber 32 is in opencommunication with the manifold 34 by means of a large opening 46through the top wall of the manifold. However, it will be understoodthat the top wall of the manifold can be provided with a plurality ofsmall holes rather than the large opening 46. Similarly, the top wall ofthe manifold portion 34a is provided with an opening 47 to receive thequantity of air fuel mixture from the manifold 34. Similarly, this largeopening 47 can be replaced by a top wall portion having a plurality ofsmall holes formed therein. The air fuel mixture from the chamber 32 isillustrated by the plurality of arrowed lines directed through themanifold.

The bottom wall of the manifold portion 34a is provided with a pluralityof threaded members 38, they being nutlike units or the like secured, asfor example. by welding to the inner wall portion of the manifold. Thethreaded units 48 receive burner units 49 therein, the burners beingdirected downwardly toward a radial heating element 50 and a flamedeflector 80. Each of the burner units 49 includes the radiant heatingelement 50 upon which the open flame of the burner is impinged so thatthe flame heat produced by the burner is converted to radiant heat. Theradiant heating elements 50 cause the pavement to be heated to a depthof approximately 1 inch or more, this being indicated by the portion 52of the pavement shown in FIG. 3. Preferably, the radiant heatingelements 50 are formed of screen-like members of lnconel material whichis a nickel-based, heat-and-oxidation-resistant material havingapproximately 13 percent chromium, 6 percent iron and small amounts ofmanganese, silicon and copper. It will be understood that other similarradiant heating material may be utilized if desired.

Also mounted within the heating chamber 28 is a preheater unit 53 which,as mentioned above, has a fuel input line 44a connected to one portionthereof and the fuel output line 44 connected to the fuel mixing chamber32. The preheater unit 53 substantially increases the temperature of thefuel before it is delivered to the mixer chamber 32 so that maximumexpansion of the fuel is obtained before combustion thereof.

Referring now to FIG. 4 there is seen a detailed sectional view of theair flow control valve 42 which is connected in the output portion 33aof the blower 33. The air flow control valve 42 includes a fixed flangeportion 56 formed on the rectangular conduit section 57. A plurality ofholes 58 are formed near the periphery of a portion of the flange 56 toreceive a pin 59 secured to an extended handle portion 60. The handle isused to rotate a vein element 61 so that a port 62 therethrough ispositioned either in line or transverse to the flow path through theconduit section 57. The hot air inlet 43 is positioned below theadjustable vein 61 and admits a quantity of heated exhaust air from oneof the vertical exhaust stacks 36, FIG. 2. While a cross vein type ofair flow control device is shown herein, it will be understood that anysuitable air flow control mechanism can be used in its place.

Referring now to FIG. 5 there is seen an elevational sectional view ofone of the burner units 49 which is mounted within the heating chamber28. Here it can be seen that the threaded fastener 48 has a meteringorifree 69 substantially in alignment with the opening through a pipe70. Air fuel mixture within the manifold 34a is delivered through themetering orifice 69 and the pipe 70 to an enlarged chamber portion of acylinder 72. Within the cylinder 72 is mounted a baffle element 73 whichhas an enlarged aperture 74 centrally thereof. The baffle 73 servesfurther to agitate and mix the air fuel mixture before it is deliveredto the lower burning portion of the cylinder 72 where the air fuelmixture is ignited. Secured to the bottom peripheral portion of thecylinder 72 are a plurality of support plates 76 having upwardly turnedend portions 77a and radially outwardly turned portions 77b for securingto the cylinder and radiant heating element 50, respectively. Thesupport legs 76 are secured by nut and bolt fasteners 78, which mayinclude suitable'washer elements as desired. The flame from the cylinder72 is directed toward a deflector element 80 which has a curved surfaceexposed to the flame so that the flame is directed radially outwardlyacross the resultant heating element 50 to more efficiently heat thesame. The deflector element 80 is mounted to the screen by means of abolt 81 and nut 82.

The deflector element 80 may take several different configurations tocause the flame to be directed radially outwardly over the screenelement. For example, FIG. 6 shows an alternate form of a detectorelement which is designated generally by reference numeral 80a. Thedeflector element 80a, in this instance, is mounted below the radiantheating element 50 so that the aperture thereof is in close proximity tothe nut 82 rather than the head of the bolt 81.

FIG. 7 illustrates the orientation of the various radiant heatingelements 50, they being substantially square in configuration andarranged diagonally within the heating chamber 28, this being shown inthe broken away portion of the drawing of FIG. 7. This type ofconfiguration insures that maximum radiant heating is directed towardthe pavement beneath the same. Also shown in FIG. 7 is the detail of thepreheater unit 53,

y it being formed of a plurality of windings of tubular ma- 7 manifoldand blower element units are designated with a prime adjacent each ofthe numbers.

The method of this invention is carried out by the apparatus describedhereinabove to more efficiently heat the road surface over which theroad resurfacing machine travels. Mixing air and fuel into the rightcombustible quantities takes place within the mixing chamber 32. Theburning of the fuel occurs at the burners 49 after the fuel is deliveredthereto through the appropriate manifold path. The flame is directedtoward the road surface and then redirected radially outwardly over aradiant heating element positioned immediately beneath the nozzle of theburner. The heating of the road surface is accomplished substantiallyprimarily by radiant heating in the wavelength range beginning in themiddle of the visible spectrum and extending to both sides of the lowerlimit of visibility. The volume of air supplying the burners can beadjusted by varying the valve mechanism 42 and fuel preheating isobtained by the coil of tubular material 53 positioned within theheating chamber. The flame from the fuel burners is re-- directed so asnot to unduly blanket the radiant heat from the radiant heating elementsnor from the top wall of the heating chamber. Also, the volume of fuelair mixture is controlled so as to maintain a blanket of radiant heatwithin the chamber and which radiant heat is not insulated by an openflame.

The radiant heating element used in accordance with the principles ofthis invention can be mounted to a small tractor or the like fortransporting the heating unit over a road surface so that spot repairwork can be accomplished.

It will be understood that other structural configurations can beincorporated when carrying out the method of this invention. Therefore,variations and modifications may be effected without departing from thespirit and scope of the novel concepts as defined by the appendedclaims.

The invention is claimed as follows:

1. A method of heating a portion of a roadway comprising the steps of;mixing air and fuel into a combustible mixture, delivering the air andfuel mixture to a plurality of burner nozzles, burning the fuel withinsaid nozzles, directing the flame from the nozzles toward the surface ofthe roadway to be heated, redirecting the flame radially outwardly fromeach nozzle so as to form a continuous wall of flame above the roadwayto be heated, said redirected flame passing above radiant heaterelements and heating the same, generating radiant heat from said radiantheater elements for heating the roadway therebeneath 'with substantiallyentirely intense radiation in the wavelength range beginning in themiddle of the visible spectrum and extending to both sides of the lowerlimit of visibility and exhausting the products of combustion producedby said flame from a position above said radiant heater elements.

2. The method of heating a portion of a roadway according to claim 1further including the step of adjusting the air supply delivered to theair fuel mixture so that the combustible mixture is delivered to thenozzles at a rate to minimize pressure within a heating chambercontaining the nozzles.

3. The method of heating a portion of a roadway according to claim 1further including the step of preheating the fuel before it is mixedwithair and delivered to the nozzles, said preheating substantiallyexpanding the fuel to minimize rapid expansion of the fuel uponcombustion at said nozzles.

4. The method of heating a portion of a roadway according to claim 1further including deflecting the flame from the nozzles immediatelyabove said radiant heating element associated therewith, said deflectingof the flame causing turbulence and upwardly turning vortex movement ofthe flame above the radiant heating element means such that no openflame impinges upon the road surface being heated.

5. The method of heating a portion of a roadway according to claim 1wherein the step of heating the roadway is accomplished for a period oftime under radiant heat sufficient to cause heat penetration to 1 inchor more beneath the surface of the roadway.

6. A method of heating a portion of a roadway comprising the steps ofdirecting a flame above a roadway in close proximity thereto, activatinga radiant heating element with said flame and heating the roadway byradiant from said element, and guiding said flames out of directimpingement against the roadway and away from between the radiantheating element and the roadway to avoid interference with saidradiation, by exhausting the products of combustion from a positionabove said radiant heater element.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 07 ,86 Dated April 30 1974 Inventor (s) EARL F CUTLER It is certified thaterror appears, in the aboveidentified patent and that said LettersPatent are hereby corrected as shown below:

Col. 6, line 33, before "portions" insert ---bottom--- Col. 6, line 40,change "resultant" to ---radiant--- Col. 6, line 47, change "detector"to ---deflector--- C01. 8, line 39-40, change "ra-diant" to--=--radiation--- C01. 8, line 40, change "flames" to ---flame----Signed d sealed this 1st day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents l FORM po'mso (10-69) USCOMM-DC 60376-P69 v 9 Hi5. GOVERNMENTPRINTING OFFICE: I969 O3GG-33l

1. A method of heating a portion of a roadway comprising the steps of;mixing air and fuel into a combustible mixture, delivering the air andfuel mixture to a plurality of burner nozzles, burning the fuel withinsaid nozzles, directing the flame from the nozzles toward the surface ofthe roadway to be heated, redirecting the flame radially outwardly fromeach nozzle so as to form a continuous wall of flame above the roadwayto be heated, said redirected flame passing above radiant heaterelements and heating the same, generating radiant heat from said radiantheater elements for heating the roadway therebeneath with substantiallyentirely intense radiation in the wavelength range beginning in themiddle of the visible spectrum and extending to both sides of the lowerlimit of visibility and exhausting the products of combustion producedby said flame from a position above said radiant heater elements.
 2. Themethod of heating a portion of a roadway according to claim 1 furtherincluding the step of adjusting the air supply delivered to the air fuelmixture so that the combustible mixture is delivered to the nozzles at arate to minimize pressure within a heating chamber containing thenozzles.
 3. The method of heating a portion of a roadway according toclaim 1 further including the step of preheating the fuel before it ismixed with air and delivered to the nozzles, said preheatingsubstantially expanding the fuel to minimize rapid expansion of the fuelupon combustion at said nozzles.
 4. The method of heating a portion of aroadway according to claim 1 further including deflecting the flame fromthe nozzles immediately above said radiant heating element associatedtherewith, said deflecting of the flame causing turbulence and upwardlyturning vortex movement of the flame above the radiant heating elementmeans such that no open flame impinges upon the road surface beingheated.
 5. The method of heating a portion of a roadway according toclaim 1 wherein the step of heating the roadway is accomplished for aperiod of time under radiant heat sufficient to cause heat penetrationto 1 inch or more beneath the surface of the roadway.
 6. A method ofheating a portion of a roadway comprising the steps of directing a flameabove a roadway in close proximity thereto, activating a radiant heatingelement with said flame and heating the roadway by radiant from saidelement, and guiding said flames out of direct impingement against theroadway and away from between the radiant heating element and theroadway to avoid interference with said radiation, by exhausting theproducts of combustion from a position above said radiant heaterelement.